A common way of packaging many commercial products is to seal the product within a close fitting plastic film. This packaging is presently accomplished by loosely wrapping the article to be packaged in a heat shrinkable plastic film, sealing the abutting edges of the film to include the product and subjecting the package to sufficient heat to activate the shrinkage of the plastic film tightly around the product, producing a tightly wrapped package.
Machines commonly referred to as L-Sealers are commercially available to accomplish the preliminary wrapping procedure as above-described. Heat shrinkable plastic film in continuous sheets, pre-folded along the central longitudinal axis and packaged in convenient rolled form are utilized for this purpose. L-Sealing machines characteristically provide a sealing table for supporting the plastic film around the product, which is inserted between the folds of the film and a pair of L-shaped jaws at the table adapted for receiving and grippingly engaging the film therebetween. One of the jaws is provided with a heated wire sealing arrangement to simultaneously sever and seal the film along a continuous L-shaped seal line extending parallel to the folded edge of the film and transversely between the parallel seal extent and the folded edge. In a continuous operation the seal formed in making each package provides the initial transverse seal to the next package so that each L-sealing operation provides complete package formation.
The operation of heating the package formed in the L-sealing operation is carried out in a machine commonly referred to as a shrink tunnel. Such machines provide a substantially enclosed heating chamber though which travels a driven conveyor belt that transports the sealed package through the heating chamber for shrinkage of the plastic film.
The initial act of wrapping performed by the L-sealer tends to capture a small quantity of air between the wrapping and the package. Machines currently exist that produce perforations within the wrapping to allow this air to escape during the shrinking process, thus preventing the bursting of the wrap. An example of such an apparatus is disclosed in U.S. Pat. No. 5,015,325.
However, many products are delivered to the sealing tunnel that have not yet settled. For example, in the textile industry, the old method of folding sheets for packaging involved manually folding and compressing the sheets. It is the current practice to employ machines to perform the folding. Many of these folding machines are incapable of performing the compression step, and thus deliver to the packaging line loosely folded sheets. Even where the folding machines are capable of compressing the sheets, the time allowed between the folding and packaging steps is sufficient to allow them to "rise". Processing these loose sheets through current shrink wrapping machinery, produces packages that have varying degrees of "free space" and thus vary considerably in volume. Even where the product is fully compressed upon delivery to the shrink tunnel, the hot air inside the tunnel causes air trapped within the folds of the sheet to expand, producing variable amounts of free space in the final package.
The variance in the free space of textile packages is most typically seen as differences in height. As can be readily understood, this creates problems in shipping when the packaged sheets are boxed in preparation for delivery. It is not uncommon for a stack of packages of sheets to be manually compressed two inches in order to force the stack into the confines of a shipping container. This compression obviously wrinkles the sheets and bends the J-insert, diminishing the appeal to customers.
Boxed products are also difficult to package attractively. The air naturally contained within a box is expanded by the heat within the shrink tunnel. When the air cools the volume of the box diminishes, loosening the wrapping. Not only is this unattractive but the chance of the wrapping tearing during shipping is increased.
Another problem which occurs during the packaging process is where flimsy products, such as leaflets, are bent due to the shrinking action of the wrap. There currently exists no practicable automated method for ensuring such bending does not happen.